Today portable electronic apparatuses, such as smartphones and tablet terminals, are in widespread use and such electronic apparatuses increasingly provide enhanced multi-functionality and technical advantages. Along with multi-function and high-performance enhancement, processors, wireless interfaces, and other components used in an electronic apparatus generate an increased amount of heat. On the other hand, it is not easy to improve the cooling capacity of the electronic apparatus due to shape constraints. Therefore, long-time use of the components under high load results in insufficient cooling, which is likely to transfer heat from the components to the housing surface of the electronic apparatus, thus increasing the surface temperature.
When the surface temperature exceeds a threshold, it is preferable to reduce the surface temperature by controlling the operating level of components, for example, decreasing the operation speed of a processor and the transmission rate of a wireless interface. Due to shape constraints, however, it is sometimes difficult to dispose a temperature sensor for directly measuring the surface temperature near the housing surface. In view of the problem, some methods have been examined that indirectly estimate the surface temperature from other measured data, such as the internal temperature of the electronic apparatus.
For example, there has been proposed a handheld medical device that reduces the surface temperature by deactivating one or more components when an estimate of the surface temperature exceeds a threshold. The proposed handheld medical device measures the temperature at a plurality of internal locations using a plurality of temperature sensors and estimates the surface temperature based on the measured temperatures and a predetermined thermal model. In addition, the proposed handheld medical device measures the amount of power consumed by components of the handheld medical device. The handheld medical device then estimates the amount of heat generated by the components based on the measured power consumption and estimates the surface temperature based on the estimated amount of heat.
International Publication Pamphlet No. WO 2012/049238
Electronic apparatuses may have therein a plurality of components generating a large amount of heat, that is, a plurality of heat sources. In estimating the surface temperature of an electronic apparatus with a plurality of heat sources, it is preferable to measure the temperature at a plurality of internal locations using a plurality of temperature sensors in order to achieve higher estimation accuracy. In this regard, how to estimate the surface temperature based on the measured temperatures obtained at the internal locations becomes a problem.
There is a delay when heat from a heat source is transferred to a temperature sensor or to the housing surface, and the delay depends on a heat transfer path (thermal path). Therefore, even if the heat source undergoes a rapid temperature change, the temperature measured by the temperature sensor and the surface temperature of the housing do not change rapidly, and transient response is observed under unsteady state conditions. For example, although the heat source undergoes a rapid increase in temperature, the surface temperature may be elevated slowly.
As a method to estimate the surface temperature with higher estimation accuracy, it may be considered appropriate to take account of transient responses in individual thermal paths from a plurality of heat sources to a plurality of temperature sensors and transient responses in individual thermal paths from the heat sources to the housing surface. One conceivable way to do this would be to calculate in advance values of a parameter (for example, the thermal time constant) representing the transient responses in the individual thermal paths and estimate the surface temperature using the parameter values and temperatures measured by the temperature sensors. However, rigorous representation of the transient responses using such a large number of parameter values involves significant computational effort to estimate the surface temperature. Especially, because the temperature measured by each temperature sensor is subject to the influence of a plurality of heat sources, the inverse calculation of the transient responses using the temperatures measured by a plurality of temperature sensors presents significant computational challenges.